<p>Although online argumentation provides students with sufficient time to think, they often lack a clear argument structure and timely guidance during the process. This may negatively affect students’ abilities to support or rebut arguments and to develop their critical thinking skills. In this study, 64 sophomores were evenly assigned to either a control or an experimental group. Each group was further divided into four teams, with each team comprising both a pro and a con side; the former needed to argue for a given position and the latter against that position. Using the collaborative online platform “ShiMo,” the control group engaged in textual argumentation, whereas the experimental group conducted their argumentation by drawing argument maps (AMs). Furthermore, students could also seek assistance from ChatGPT 3.5 when encountering difficulties in creating AMs. Both questionnaires and content analysis were used to evaluate students’ critical thinking skills and perceptions. The findings indicated that ChatGPT and AM-supported online argumentation effectively promoted students’ critical thinking skills, encouraging them to engage in more rebuttal activities through analysis, evaluation, and creation. Students perceived that AMs clearly visualized argument structure, albeit providing limited assistance in facilitating information gathering. ChatGPT provided detailed information and fostered a positive attitude toward argumentation among students; however, the accuracy and appropriateness of the provided information remained doubtful. These findings have several implications. College students’ critical thinking skills can be improved by integrating teacher guidance into ChatGPT and AM-supported online argumentation, being skeptical of ChatGPT’s outputs, and improving information literacy to efficiently utilize ChatGPT.</p>